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National's Auckland Central MP Nikki Kaye also faced a chorus of boos when she spoke and struggled to be heard.

When Mr Key arrived at the event, the protesters threw a large pile of glitter at him, which struck him in the face. He said afterwards that he had expected the reaction.

He downplayed the protest, saying it was from a small group of individuals who did not support the National-led Government.

Mr Key has attended the past 10 Big Gay Out events. He has been jeered on previous occasions, but has mostly been met with a positive reception, in particular after he spoke in favour of legalising same-sex marriage in 2012.

Since the Trans-Pacific Partnership (TPP) was signed on February 4, Mr Key has had a mixed reception at his public outings.

He was forced to avoid Waitangi Day commemorations for the first time since becoming Prime Minister, in part because of Maori anger about the TPP.

Instead, he attended the Nines league event in Auckland, where he was booed by a small section of the crowd. A trip to Wairarapa on Thursday was without incident, as was a visit to Christchurch on Saturday.

Public roadshows on the Trans-Pacific Partnership begin next month, with the first one in Auckland on March 7. Registration will be required for the event, but a Ministry of Foreign Affairs spokesman said this was not a measure to vet for potential protesters.

A police spokeswoman said police were speaking with the Ministry of Foreign Affairs and Trade (Mfat) about the roadshows.

"As was seen in Auckland during the signing of the TPP, the role of police is to balance the lawful right to protest while appropriately managing any safety and security issues which may arise," the spokeswoman said.

Before the TPP signing, police door-knocked activists to ask about their plans for the event.

Large protests on the day shut down parts of Auckland's roading network and led to the cancellation of a vineyard event for TPP trade ministers.